Olenellus gilberti trilobite fossil. Trilobites were arthropods that fed as they crawled on the seabed. They are now extinct. This trilobite species was described in 1874 by the US geologist and palaeontologist Fielding Bradford Meek (1817-1876). The fossil dates from the Lower Cambrian period (510 to 540 million years ago), and was found in the Chisolm shale section of the Pioche formation, in Nevada, USA. This specimen is part of a collection maintained by Pete Lawrence.